Aircraft utilize antenna and associated antenna support equipment to transmit, receive and download data communication signals. Aircraft antenna(s) are typically surface mounted on the outer fuselage of the aircraft. Aerodynamic drag concerns require the antenna(s) be shaped to reduce drag on the aircraft. Associated equipment is normally located inside the aircraft on support structures developed for this purpose.
When new systems or technologies are developed or additional communication system equipment is required on an aircraft, additional space must normally be found inside the aircraft for the associated support equipment. On commercial aircraft in particular, space is often created for this equipment in the overhead compartments, and in particular, over the walkways (i.e., central or side aisle-ways) of the aircraft. The drawback of using this space is its constraint on overhead height in the aircraft walkways.
Another problem exists on current aircraft that employ phased array communication antennas. Most currently employed phased array antennas operate at low voltage, i.e., three to six volts direct current (DC). This low voltage requires a correspondingly high current to operate the antenna system. Drawbacks to carrying high current include increased cabling weight between the antennas and their power transformers, and power loss due to heat generation and subsequent transmission loss. In an exemplary application currents as high as about 90 amperes must be carried. A 90 ampere current rating requires a cable size of about four gauge, American Wire Gauge (AWG) be used. Even with this size wire, however, cable heat and power loss places a practical limit on the distance between the power supply and the antennas to about 3.1 to 4.6 meters (10 to 15 feet). This constrains the location of the antenna and/or the location of the aircraft mounted antenna support equipment.
The above problems are compounded for aircraft required to communicate via signals from satellite communication systems. These systems utilize radio frequency (RF) signals in the Ku-band frequency range, for example in the 12 to 14 gigahertz (GHz) range. RF signals on the transmit channel are normally about 14 GHz and above (up to about 44 GHz) and RF signals on the receive channel are normally about 12 GHz and above (up to about 20 GHz). In this frequency range attenuation of signal strength becomes a critical drawback as the antenna/antenna equipment and aircraft communication equipment are separated. As an exemplary loss in the RF frequency range, about every three feet of signal line length used between the antenna and down-converting equipment results in approximately 50% loss in signal strength. As a practical result, an exemplary limit now applied to control this attenuation provides that down-converters be separated by a distance of no greater than about 1.2 meters (four feet) from their respective antenna(s). This places a greater constraint on the location of both the antenna(s) and antenna support equipment than the above noted constraint due to power loss.
Further problems are created for aircraft when new communication systems, such as Connexion By BoeingSM, require one or more new antennas be installed. In the exemplary Connexion By BoeingSM system, the antennas are an intermediary subsystem between the aircraft and the ground. To incorporate the Connexion By BoeingSM system onboard an aircraft, two phased array antennas are required, and the associated support equipment for the phased array antennas, if stored within the aircraft, occupies about six boxes. In an example case of a narrow body aircraft (i.e., an aircraft having a single aisle), providing space to locate and mount eight boxes requires using space over the aircraft aisle-way. The drawback to this as noted above is reduced height along the center aisle-way of the narrow body aircraft. Wide body aircraft (i.e., two or more aisles) are constrained by addition of six boxes, but not to the same degree as narrow body aircraft.
It is aerodynamically desirable to place an antenna at the top of the aircraft fuselage along a vertical plane perpendicularly intersecting the aircraft's longitudinal axis near the leading edge of the aircraft wings. This preferred antenna location, together with the above equipment and cable length constraints, further constrains the arrangement. In an alternate arrangement, sets of antennas are provided. Multiple arrangements are possible. Two exemplary arrangements are a first fore-aft arrangement comprising two antennas and a second side-by-side arrangement of preferably four antennas. With the side-by-side arrangement, two antennas are preferably located on each side of the aircraft, to improve the field of view toward the horizon (also called a “saddlebag” configuration). Both saddlebag and fore-aft arrangement antenna configurations improve the arrangement of support equipment by spreading out the equipment, but still constrain the overall arrangement if the support equipment is all located within the aircraft.